In recent years, with growing environment awareness, the soil pollution problem caused by the disposal of plastic products and the global warming problem caused by the increase of carbon dioxide generated by incineration attract attention. Energetic R&D activities are underway to develop various biodegradable resins for addressing the former problem, and to develop resins made from plant-derived materials which do not emit a new load of carbon dioxide into the atmosphere even if they are burned, for addressing the latter problem. Also for use as shaped articles for exhibiting and packaging various commodities and as containers such as food trays and drinking cups, various biodegradable resins and resins made from plant-derived materials are being developed. Above all, especially polylactic acid as an aliphatic polyester is a plant-derived biodegradable clear plastic with a glass transition point as high as about 60° C., and attracts the highest attention as a promising material.
However, polylactic acid that is a polyester-based resin has a problem that the strength of the resin is lowered by hydrolysis. Various techniques are proposed to solve the problem.
For example, JP 7-316273 A describes a technique in which for capping the acid ends that affect hydrolysis, an aliphatic alcohol is made to coexist when a lactide or lactic acid is polymerized for producing polylactic acid as an acid end-capped polylactic acid.
JP 2007-291336 A proposes a technique of letting a polyester resin contain a reactive end capping agent and a phosphorus-based stabilizer to provide a polyester resin composition capable of holding the physical properties of the resin for a long period of time.
Further, JP 2008-7750 A describes a technique in which a buffering agent is added during the period after completion of esterification reaction or ester interchange reaction before the initial stage of polycondensation reaction, for decreasing the number of the acid ends of polyethylene terephthalate.
However, the aforementioned prior art has the following problem. In JP 7-316273 A, the acid ends of polylactic acid which affect hydrolysis are capped, but the effect of enhancing the hydrolysis resistance is not sufficient. In JP 2007-291336 A, a polyester resin is made to contain a reactive end capping agent and a phosphorus-based stabilizer, but satisfactory hydrolysis resistance is not obtained.
Further, JP 2008-7750 A describes a technique in which a buffering agent is added during the period after completion of esterification reaction or ester interchange reaction before the initial stage of polycondensation reaction for decreasing the number of acid ends of polyethylene terephthalate, but does not disclose a technique of enhancing the hydrolysis resistance of a polylactic acid-based composition.
In view of the background as described above, it could be helpful to provide a polylactic acid-based composition with excellent hydrolysis resistance.